Secondary batteries are being used as large-capacity power storage batteries for electric vehicles or battery power storage systems and small high-performance energy sources for portable electronic devices such as mobile phones, camcorders, notebooks, and the like. In order to miniaturize portable electronic devices and achieve long-term continuous use, studies on weight lightening of components and low power consumption and secondary batteries having a small size with high capacity are required.
Recently, in the secondary battery market, the development of an anode active material which enables large size, high capacity and high performance has been demanded in order to be used in portable electronic devices and information communication devices and also in energy storage devices for hybrid vehicles (HEV or PHEV) or power generation systems. However, highly crystalline carbon-based active materials commercially used as an anode active material for a conventional secondary battery have a limited theoretical capacity of 372 mAh/g despite having excellent characteristics as active materials for batteries, and, thus, the development of an improved anode active material is essential in order to develop high-capacity and high-performance lithium secondary batteries.
Silicon is an example of non-carbon-based anode active materials, and silicon (Si) has a high discharge capacity of 4,200 mAh/g and a very low lithium reaction potential of 0.4 V (Li/Li+) and is thus known to be the most suitable for an anode material. However, silicon undergoes volume expansion up to 400% upon insertion (charge) of lithium ions, and, thus, the capacity cannot be maintained, and due to a low electric conductivity or the like, silicon needs to be improved in this matter in order to be commercialized as an anode active material.
Meanwhile, Korean Patent No. 10-1248108 relates to a negative electrode for lithium ion secondary battery including an amorphous silicon oxide thin film, and discloses a method of preparing the negative electrode for lithium ion secondary battery, including forming the amorphous silicon oxide thin film of SiOx (0.3≤×≤1.5).